1. Field of the Invention
The present invention relates to an on-board vehicle control unit that controls operation of an on-board vehicle automatic device, and to a method of writing a control program and/or reference data used in execution of the program into the on-board control unit. While not intended to be so limited, the invention may be used as a transmission controller for controlling operation of an automatic transmission in a vehicle, and as a controller for control of operation of other on-board automatic devices.
2. Description of Related Art
JP-A-2003-202072 describes a control unit in a vehicle, which control unit calculates target speed based on road information and a travel condition, and which provides computer control of a vehicle automatic transmission so that vehicle speed corresponds to the target speed. JP-A-2006-283832 describes a control unit in a vehicle, which control unit uses a CPU incorporating RAM and EEPROM to control an automatic transmission based on a shift lever position and an engine operating condition.
JP-A-2001-034601 describes a method of writing a control program into a nonvolatile memory of a 1-chip microcomputer used for most on-board vehicle control units. The microcomputer mainly includes a CPU, a RAM and a nonvolatile memory (EPROM or EEPROM), wherein the RAM has a smaller storage capacity than the nonvolatile memory. In a first embodiment shown in FIG. 1 of JP-A-2001-034601, a control program is compressed in order to reduce transfer time of the control program and then transferred from an external PROM writer into (the nonvolatile memory of) the microcomputer. The control program is divided into blocks that respectively fit into free spaces of the RAM and each of the blocks is compressed and transferred. However, the program is written while being transferred, which is not suitable for high compression, leading to a low compression ratio. In addition, when the compressed data is decompressed, since the data is compressed and transferred in blocks that respectively fit into free spaces of the RAM, compressed data volume, namely, transferred data volume in a block is small, resulting in relatively little savings in transfer time. Thus, in a second embodiment, the compressed data, in blocks of the control program, is received and sequentially written into the RAM, and then written into the nonvolatile memory, and when all the compressed data of the control program has been stored in the nonvolatile memory, the compressed data is sequentially read from the nonvolatile memory into the RAM and decompressed, and then the decompressed data is then written back into the nonvolatile memory. In the foregoing process, transfer time for transfer of the control program from the PROM writer to the 1-chip microcomputer is shortened, in addition, a compression method with a high compression ratio may be used, and therefore transfer time can be further reduced.
However, since the nonvolatile memory needs to concurrently hold compressed data of a control program and decompressed data thereof, storage capacity of the nonvolatile memory must be increased in correspondence to the amount of compressed data to be held. Moreover, when the control program is written, the same compressed data is written twice into the RAM, in addition, writing and reading of the compressed data must be performed into/from the nonvolatile memory, which increases the volume handled in read/write processing of data from/into the RAM and the nonvolatile memory.
Writing of control data and/or reference data used in the control program is different in data transfer frame formed by the PROM writer or other transfer tools as between uncompressed data transfer and compressed data transfer. In addition, storing processing of data into a nonvolatile memory differs between the storing of compressed data and uncompressed data, the data being received by an on-board vehicle control unit such as 1-chip microcomputer. However, in some cases, it is desirable that all data be transferred as uncompressed data, or that the data be transferred as mixed data of compressed data and uncompressed data. Particularly, since the reference data used in the control program may be frequently changed for convenience of design, the data is sometimes desired to be processed as uncompressed data because easily confirmed. Moreover, when writing a particular identification number, uncompressed data being recognizable as text data is desirably used in some cases.